The present invention generally relates to wireless communication networks, and particularly relates to rate control in such networks.
Rate control is a form of radio link adaptation wherein the transmission rate from a transmitter to a receiver is adjusted during ongoing communications responsive to changing signal quality, network loading constraints, etc. As an example, a wireless network base station may enforce common or per-user reverse link rate control to maintain reverse link loading at or around some targeted level.
Base stations also may enforce or otherwise supervise reverse link rate control of individual mobile stations to meet Quality-of-Service (QoS) requirements that specify maximum delay or jitter limits for reverse link transmissions for particular mobile stations. For example, a given mobile station may run one or more applications, each having its own logical “service instance,” and each potentially having its own QoS requirements.
Supporting reverse link rate control in this context, the base station tracks or otherwise monitors indications of reverse link performance for each mobile station, so that it can determine when rate adjustments are required for the individual mobile stations to meet QoS or other requirements. Such monitoring requires the mobile stations to provide, i.e., transmit, reverse link information to the base station. For example, the mobile stations may provide the base station with information regarding their transmit buffer sizes as an indication of whether their reverse link rates should be adjusted upward or downward.
With this approach, for example, the base station may grant a higher reverse link rate to a mobile station that has more than a certain amount of pending transmit data buffered. In other words, a large amount of pending transmit data at the mobile station may trigger the base station to grant a higher rate for one or more subsequent transmit periods. Obviously, the base station can provide such control only when it is provided with transmit buffer information from the mobile stations. Thus, the need for additional signaling between the mobile stations and the base station is one drawback of this approach.
Another drawback stems from the approach's failure to directly indicate a pending service problem, i.e., knowledge of a given mobile's transmit buffer size does not equate to direct knowledge of whether the mobile station's reverse link performance is at risk of violating QoS or other service constraints. For example, the average reverse link throughput of the mobile station may be quite high at the current time and, thus, one would expect even a relatively large transmit buffer to drain quickly. Thus, in addition to receiving transmit buffer size reports from the mobile stations, which undesirably adds overhead signaling to the finite-capacity reverse link, the base station generally has to monitor other conditions, or calculate additional metrics, to determine whether rate adjustments are needed for particular mobile stations.